Hypocalcemia

Diagnosis

Indications for Testing

  • Suspect when symptoms occur and serum calcium is low

Laboratory Testing

  • Initial testing – serum calcium and albumin [corrected calcium = measured total calcium +0.8 (4.0-serum albumin)], serum phosphorus, serum magnesium, serum creatinine
  • If calcium low, consider repeat testing or ionized calcium
    • Ionized calcium does not need to be corrected for hypoalbuminemia, but should be corrected for pH
  • If hypocalcemia is confirmed, order intact parathyroid hormone (PTH)
    • Intact PTH
      • Elevated PTH, normal or high phosphorus, normal magnesium, high creatinine – renal failure/pseudohypoparathyroidism
      • Elevated PTH,  normal or low phosphorus, normal magnesium, normal creatinine
      • Low PTH, normal or high phosphorus, normal creatinine, low or normal magnesium – hypoparathyroidism or hypomagnesemia
      • Normal PTH, normal or low phosphorus, normal creatinine, normal magnesium, low albumin – hypoalbuminemia (pseudohypocalcemia)

Differential Diagnosis

Monitoring

  • Serum calcium, phosphorus, and creatinine – measure weekly during initial therapy, then monthly
  • Once stabilized on therapy, measure values 1-2 times/year

Clinical Background

Hypocalcemia may be noted either acutely or chronically in hospitalized patients and outpatients.

Epidemiology

  • Prevalence – occurs in 12-80% of critically ill patients

Etiology

Pathophysiology

  • Serum calcium concentration kept within a narrow physiologic range
  • Control of calcium by parathyroid hormone, vitamin D (1,25), calcium, and phosphate

Clinical Presentation

  • Acute
    • Neuromuscular – tetany, paresthesias, muscle spasms (Chvostek and Trousseau signs)
    • Neuropsychiatric – anxiety, hallucinations, confusion
    • Cardiovascular – bradycardia, ventricular arrhythmias, cardiac collapse
  • Chronic
    • Neuropsychiatric – cognitive deficits, extrapyramidal symptoms
    • Dermatologic – dermatitis, dry skin
    • Dental – enamel hypoplasia
    • Ophthalmologic – cataracts

Treatment

  • Treat according to etiology
  • Calcium analogues – may require intravenous calcium depending on calcium level
  • Vitamin D analogues

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Calcium, Serum or Plasma 0020027
Method: Quantitative Spectrophotometry
Diagnose hypocalcemia    
Albumin, Serum or Plasma by Spectrophotometry 0020030
Method: Quantitative Spectrophotometry

Order concurrent with calcium to assess for hypoalbuminemia

   
Creatinine, Serum or Plasma 0020025
Method: Quantitative Enzymatic

Evaluate renal function

   
Phosphorus, Inorganic, Plasma or Serum 0020028
Method: Quantitative Spectrophotometry

Evaluate renal function 

   
Parathyroid Hormone, Intact 0070346
Method: Quantitative Electrochemiluminescent Immunoassay
Diagnose hypoparathyroidism    
Magnesium, Plasma or Serum 0020039
Method: Quantitative Spectrophotometry
May help to determine etiology of hypocalcemia    
Vitamin D, 25-Hydroxy 0080379
Method: Quantitative Chemiluminescent Immunoassay

Preferred screening test for vitamin D deficiency

Preferred test to monitor response to supplementation

   
Calcium, Ionized, Serum 0020135
Method: Ion-Selective Electrode/pH Electrode

Diagnose hypocalcemia

Does not need to be corrected for hypoalbuminemia but should be corrected for pH

   
Additional Tests Available
 
Click the plus sign to expand the table of additional tests.
Test Name and NumberComments
Parathyroid Hormone, Intact with Calcium 0070172
Method: Quantitative Electrochemiluminescent Immunoassay

Preferred test to diagnose hypercalcemia, hyperparathyroidism

Calcium, Ionized, Whole Blood 0020140
Method: Ion-Selective Electrode/pH Electrode

Available only to University of Utah patients